A widely accepted and used water heater for residential hot water production and storage is the electric resistance water heater and storage tank. Water heaters typically include a tank defining a chamber for retention of water. A water inlet pipe that is provided with a first connection for interconnection with a cold water supply line that conveys fresh relatively cold water into the chamber. Within the tank there are electric resistance elements that heat the water in the tank. In current embodiments, there are at least two electric resistance elements. A first electric resistance element positioned near the bottom of the tank and a second electric resistance element positioned near the top of the tank. There are also two sensors positioned on the exterior of the tank that measure the temperature of the tank near the top and bottom of the tank in proximity to the location of the electric resistance elements. When the temperature sensed by such sensors drops below a certain temperature level, these sensors close the contacts associated with the corresponding electric resistance elements causing the electric resistance elements to energize.
When water is supplied to the tank, it is supplied through a dip tube that pushes the cold water to the bottom of the tank and thereby pushes the hot water out of the top through the outlet pipe where water is the hottest. One of the problems with this configuration is that the sensor near the top of the tank can't detect that hot water is exiting and cold water is entering the tank near the bottom. The lower sensor detects that cold water is entering the tank when it detects a temperature drop at the thermostat, which is the primary purpose for having two sensors. When the lower sensor detects a temperature drop below a certain level, it closes the contact and energizes the lower electric resistance element until the temperature reaches a specified level. But, each time the lower electric resistance element heats the water; the heated water is buoyant and goes up to the top of the tank. For example, if the tank is holds 50 gallons of water, and three gallons of water flow into the tank, it may cause the lower electric resistance element to be energized for a few minutes in order to recover the temperature. If a few minutes later, there is a draw of another three gallons of water, the lower electric resistance element is energized again for another few minutes in order to recover the temperature. This causes the heated water to rise to the top creating a problem called stacking. Under sequential small draws of water, the lower electric resistance element is energized each time and runs until the lower sensor is satisfied that the lower part of the tank is sufficiently warm. When this is occurring, the top part of the tank continues to get a little bit hotter each time which causes over heating of water in the top of the tank, which can potentially lead to undesirably hot water being drawn from the tank. So there is a need for a configuration that solves the problem associated with stacking resulting from small sequential water draws made on current water heaters.